Economical and Efficient Hybrid Surfactant with Low Fluorine Content for the Stabilisation of Water-in-CO2 Microemulsions

• Facile and economic synthesis of hybrid AOT analogue surfactants.
• Hybrid surfactants with low fluorine content.
• Surfactant performances in CO2 affected by chain branching.
• Hybrids with high degree of branching demonstrate high solubilising power.
• Hybrid CF2/SIS1 is as effective and efficient as fluorinated surfactant.

The relationship between the tail architecture and performance of hybrid AOT analogue surfactants has been investigated. Three hybrid surfactants were synthesised using hydrocarbon CO2-philic tails with different levels of chain branching. The performance of each surfactant was investigated via high-pressure phase behaviour, UV-visible spectroscopy, and air–water (a/w) surface tension measurements. Notably, the incorporation of hydrocarbon CO2-philic tails with a high degree of branching has been found to significantly boost CO2-philicity, allowing the surfactant to stabilise water-in-CO2 (w/c) microemulsions at low cloud pressures, Ptrans. The newly synthesised hybrid CF2/SIS1 (sodium (4H, 4H, 5H, 5H, 5H-pentafluoropenyl-5,7,7-trimethyl-2-(1,3,3-trimethyl-buthyl)-octyl)-2-sulfosuccinate) is a CO2-philic surfactant that contains the lowest amount of fluorine (15.01 wt%) and exhibits the highest efficiency of any di-chain surfactant to date. High-pressure phase behaviour studies provided a maximum water-to-surfactant molar ratio (wmax) of wmax = 39, which is usually only observed from surfactants with long fluorocarbon chains. The present results are beneficial for expanding the pool of economical, effective, and efficient surfactants available for CO2-based technology.

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